Foamed cement compositions and associated methods of use

ABSTRACT

A method is provided for reducing the density of a well cement composition for cementing in a subterranean formation. The method comprises providing a cement composition that comprises water and a cement, and then adding an additive comprising an anionic foam stabilizer and an anionic foaming agent or a Zwitterionic foam booster. A gas is added to this mixture to reduce the density. Further, foamed cement compositions and additives for foaming and stabilizing a well cement composition are provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/946,979 filed Sep. 22, 2004, entitled “Foamed Cement Compositions andAssociated Methods of Use,” the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

The present invention relates to subterranean cementing operations andassociated methods, and more particularly, to foamed cement compositionsthat comprise an additive, the additive comprising an anionic foamstabilizer and at least one of an anionic foaming agent or aZwitterionic foam booster.

Hydraulic cement compositions commonly are utilized in subterraneanoperations, particularly subterranean well completion and remedialoperations. For example, hydraulic cement compositions may be used inprimary cementing operations, whereby pipe strings such as casings andliners are cemented in well bores. In performing primary cementing,hydraulic cement compositions may be pumped into an annular spacebetween the walls of a well bore and the exterior surface of a pipestring disposed therein. The cement composition is permitted to set inthe annular space, thereby forming an annular sheath of hardenedsubstantially impermeable cement therein that substantially supports andpositions the pipe string in the well bore, and that bonds the exteriorsurface of the pipe string to the walls of the well bore. Hydrauliccement compositions also are used in remedial cementing operations thatinvolve plugging highly permeable zones or fractures in well bores,plugging cracks and holes in pipe strings, and the like.

Cement compositions utilized in subterranean operations may belightweight to prevent excessive hydrostatic pressure from being exertedon subterranean formations penetrated by the well bore, whereby theformations may be unintentionally fractured. One type of lightweightcement composition is a foamed cement composition, i.e., a cementcomposition that comprises a gas. In addition to being lightweight, thegas contained in the foamed cement composition improves the ability ofthe composition to maintain pressure and prevent the flow of formationfluids into and through the cement composition during its transitiontime, i.e., the time during which the cement composition changes from atrue fluid to a set mass. Foamed cement compositions are alsoadvantageous because they have low fluid loss properties and may act toprevent the loss of fluid circulation. Additionally, foamed cementcompositions when set have a lower modulus of elasticity than non-foamedcements, which is often desirable as it enables the resultant setcement, inter alia, to resist hoop stresses exerted on the set cement inthe annulus.

A foamed cement composition generally may be prepared by mixing a gas,such as air or nitrogen, with the cement composition. Foamed cementcomposition typically further may comprise a variety of surfactantscommonly referred to as “foaming agents” for facilitating the foaming ofa cement composition and various other surfactants commonly referred toas “foam stabilizers” for preventing the components of the foamed cementcomposition from prematurely separating. While a variety of foamingagents and foam stabilizers are well known in the art, problems havebeen associated with their use. For example, certain foaming agents,such as those consisting of a surfactant of Formula 1,R—(OR′)_(n)—OSO₃—X⁺, and foam stabilizers, such as a glycol of Formula2, CH₃O—(CH₂CH₂O)_(n)H, or a betaine surfactant, may lower thecompressive strength of the resultant set cement composition.Furthermore, upon mixing, the foaming agents and foam stabilizers usedheretofore with water, gelation may occur, which is undesirable.Moreover, some foaming agents and/or foam stabilizers may haveundesirable environmental characteristics and/or may be limited bystrict environmental regulations in certain areas of the world.

SUMMARY

The present invention relates to subterranean cementing operations andassociated methods, and more particularly, to foamed cement compositionsthat comprise an additive, the additive comprising an anionic foamstabilizer and at least one of an anionic foaming agent or aZwitterionic foam booster.

In one embodiment, the present invention provides a method of cementingin a subterranean formation that comprises providing a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising an anionic foaming agent and an anionic foamstabilizer; placing the cement composition into the subterraneanformation; and allowing the cement composition to set therein. In someembodiments, the additive further may comprise a Zwitterionic foambooster.

In another embodiment, the present invention provides a method ofcementing in a subterranean formation that comprises providing a foamedcement composition that comprises water, a cement, a gas, and anadditive, the additive comprising a Zwitterionic foam booster and ananionic foam stabilizer; placing the cement composition into thesubterranean formation; and allowing the cement composition to settherein. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment, the present invention provides a method ofreducing the density of a cement composition that comprises providing acement composition that comprises water and a cement; adding an additiveto the cement composition, the additive comprising an anionic foamingagent and an anionic foam stabilizer; and adding a gas composition tothe cement composition. In some embodiments, the additive further maycomprise a Zwitterionic foam booster.

In another embodiment, the present invention provides a method ofreducing the density of a cement composition that comprises providing acement composition that comprises water and a cement; adding an additiveto the cement composition, the additive comprising a Zwitterionic foambooster and an anionic foam stabilizer; and adding a gas to the cementcomposition. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment the present invention provides a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising an anionic foaming agent and an anionic foamstabilizer. In some embodiments, the additive further may comprise aZwitterionic foam booster.

In another embodiment the present invention provides a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising a Zwitterionic foam booster and an anionic foamstabilizer. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment, the present invention provides an additive forfoaming and stabilizing a cement composition that comprises an anionicfoaming agent and an anionic foam stabilizer. In some embodiments, theadditive further may comprise a Zwitterionic foam booster.

In yet another embodiment, the present invention provides an additivefor foaming and stabilizing a cement composition that comprises aZwitterionic foam booster and an anionic foam stabilizer. In someembodiments, the additive further may comprise an anionic foaming agent.

The features and advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the descriptionof the specific embodiments that follows.

DESCRIPTION

The present invention relates to subterranean cementing operations andassociated methods, and more particularly, to foamed cement compositionsthat comprise an additive, the additive comprising an anionic foamstabilizer and at least one of an anionic foaming agent or aZwitterionic foam booster.

The foamed cement compositions of the present invention generallycomprise water, a cement, a gas, and an additive of the presentinvention. Generally, the additive of the present invention comprises ananionic foam stabilizer and at least one of an anionic foaming agent ora Zwitterionic foam booster. In one embodiment, the additive of thepresent invention comprises an anionic foam stabilizer and an anionicfoaming agent. In another embodiment, the additive of the presentinvention comprises an anionic foam stabilizer and a Zwitterionic foambooster. In yet another embodiment, the additive of the presentinvention comprises an anionic foam stabilizer, an anionic foamingagent, and a Zwitterionic foam booster.

Generally, the foamed cement compositions of the present invention mayhave a density sufficient for a particular application as desired by oneof ordinary skill in the art. In some embodiments, the foamed cementcompositions of the present invention have a density in the range offrom about 2 pounds per gallon (“ppg”) to about 20 ppg. In certainembodiments, the foamed cement compositions of the present invention mayhave a density in the range of from about 10 ppg to about 15 ppg.

The water utilized in the foamed cement compositions of the presentinvention may be fresh water, saltwater (e.g., water containing one ormore salts dissolved therein), brine (e.g., saturated saltwater),seawater, or combinations thereof. Generally, the water may be from anysource provided that it does not contain an excess of compounds (e.g.,dissolved organics) that may adversely affect a foamed cementcomposition of the present invention. Further, the water may be presentin an amount sufficient to form a pumpable slurry. In certainembodiments, the water may be present in the foamed cement compositionsof the present invention in an amount in the range of from about 16% toabout 200% by weight of the cement (“bwoc”) therein. In certainembodiments, the water may be present in the foamed cement compositionsof the present invention in an amount in the range of from about 25% toabout 90% bwoc therein. In certain embodiments, the water may be presentin the foamed cement compositions of the present invention in an amountin the range of from about 28% to about 45% bwoc therein. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of water for a chosen application.

Any cements suitable for use in subterranean applications may besuitable for use in the present invention. In certain embodiments, thefoamed cement compositions of the present invention comprise a hydrauliccement. A variety of hydraulic cements may be suitable for use,including those comprising calcium, aluminum, silicon, oxygen, and/orsulfur, which set and harden by reaction with water. Such hydrauliccements include, but are not limited to, Portland cements, pozzolaniccements, gypsum cements, soil cements, calcium phosphate cements, highalumina content cements, silica cements, high alkalinity cements, andmixtures thereof.

The gas utilized in the foamed cement compositions of the presentinvention may be any gas suitable for foaming a cement composition,including, but not limited to, air or nitrogen. Generally, the gasshould be present in the foamed cement compositions of the presentinvention in an amount sufficient to form a foam. In certainembodiments, the gas may be present in the foamed cement compositions ofthe present invention in an amount in the range of form about 5% toabout 55% by volume of the foamed cement composition therein atatmospheric pressure. In another embodiment, the gas may be present inthe foamed cement compositions of the present invention in an amount inthe range of form about 15% to about 30% by volume of the foamed cementcomposition therein at atmospheric pressure.

The foamed cement compositions of the present invention also include anadditive of the present invention, the additive comprising an anionicfoam stabilizer and at least one of an anionic foaming agent or aZwitterionic foam booster. Among other things, the additive of thepresent invention should facilitate the foaming of a non-foamed cementslurry and also act to stabilize the foamed cement composition formedtherewith. In one embodiment, the additive of the present inventioncomprises an anionic foam stabilizer and an anionic foaming agent. Inanother embodiment, the additive of the present invention comprises ananionic foam stabilizer and a Zwitterionic foam booster. In yet anotherembodiment, the additive of the present invention comprises an anionicfoam stabilizer, an anionic foaming agent, and a Zwitterionic foambooster.

Generally, the additive of the present invention may be present in thefoamed cement compositions in a sufficient amount to foam and stabilizea foamed cement composition of the present invention. In someembodiments, the additive of the present invention may be present in thefoamed cement compositions of the present invention in an amount in therange of from about 0.01% to about 5% by volume of the water (“bvow”)therein. In certain embodiments, the additive of the present inventionmay be present in the foamed cement compositions of the presentinvention in an amount in the range of from about 0.5% to about 2% bvowtherein.

The anionic foam stabilizer suitable for use in the additives of thepresent invention may be any anionic foam stabilizer capable ofstabilizing a foamed cement composition, e.g., by preventing componentstherein from separating and preventing foam break, that does notaversely affect other components of a foamed cement composition of thepresent invention. Examples of suitable anionic foam stabilizers includefatty methyl ester surfactants and aliphatic alkyl sulfonate or sulfatesurfactants having an alkyl chain length of from about 16 to about 22carbons. Examples of suitable fatty methyl ester surfactants include,but are not limited to, a fatty methyl ester sulfonate (“MES”)surfactant. Commercially available examples of suitable anionic foamstabilizers include, but are not limited to, a palm oil MES from HuishDetergents, Inc., Salt Lake City, Utah; a fatty MES from Lion Chemicals,Tokyo, Japan; and MES from Baker Petrolite, Sugarland, Tex. The anionicfoam stabilizer is typically present in the additives of the presentinvention in an amount in the range of from about 0.01% to about 90% byweight of the additive. In certain embodiments, the anionic foamstabilizer may be present in the additives of the present invention inan amount in the range of from about 0.1% to about 20% by weight of theadditive. Inclusion of larger amounts of the anionic foam stabilizer inrelation to the other components of the additive of the presentinvention may have a dispersing effect on a foamed cement composition ofthe present invention. For example, inclusion of the anionic foamstabilizer in an additive of the present invention in an anionic foamingagent-to-Zwitterionic foam booster-to-anionic foam stabilizer weightratio of up to about 2:1:1 may have a dispersing effect on a foamedcement composition of the present invention. One of ordinary skill inthe art should be able to determine the appropriate amount of theanionic foam stabilizer to include in an additive of the presentinvention for a particular application.

The anionic foaming agent suitable for use in the additives of thepresent invention may be any anionically charged surfactant capable offoaming an aqueous-based fluid. Furthermore, the anionic foaming agentshould not adversely affect other components in a foamed cementcomposition of the present invention. Examples of suitable anionicfoaming agents include, but are not limited to, sulfate surfactants andsulfonate surfactants. In some embodiments, the sulfate surfactant maybe an alkyl ether sulfate surfactant (“AES”). In certain of theseembodiments, the alkyl ether sulfate surfactant may be an ethoxylatedalcohol ether sulfate surfactant of Formula 3:H(CH₂)_(a)(OC₂H₄)_(b)OSO₃X⁺wherein a is an integer in the range of from about 6 to about 14, b isan integer in the range of from about 3 to about 10, and X is anycompatible cation. In other embodiments, the sulfonate surfactant may bean alpha-olefinic sulfonate (“AOS”) surfactant. In certain of theseembodiments, the alpha-olefinic sulfonate surfactant may be of Formula4:H(CH₂)_(n)—CH══CH—(CH₂)_(m)SO₃X⁺wherein n is an integer in the range of from about 3 to about 12, m isan integer in the range of from about 3 to about 12, and X is anycompatible cation. An example of a suitable AOS surfactant iscommercially available as “WITCONATE™” foamer from Akzo Nobel,Stratford, Conn. Examples of suitable AES surfactants are commerciallyavailable as “SULFOCHEM®” alkyl ether sulfates from Chemron, PasoRobles, Calif. Where present, the anionic foaming agent may be presentin the additives of the present invention in an amount in the range offrom about 0.01% to about 90% by weight of the additive. In certainembodiments, the anionic foaming agent may be present in the additivesof the present invention in an amount in the range of from about 30% toabout 70% by weight of the additive.

The Zwitterionic booster suitable for use in the additives of thepresent invention may be any Zwitterionic surfactant capable of foamingan aqueous-based liquid. Furthermore, the Zwitterionic booster shouldnot adversely affect other components in a foamed cement composition ofthe present invention. Examples of suitable Zwitterionic boostersinclude, but are not limited to, betaine surfactants, sulfobetainesurfactants, amphopropionate surfactants, and glycinate surfactants. Incertain embodiments, the betaine surfactant is a fatty betainesurfactant. In one embodiment, the Zwitterionic booster comprises analkyl or alkene amidopropyl betaine surfactant of Formula 5:R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂COO⁻wherein R is an alkyl chain of from about 6 to about 18 carbons ormixtures thereof. Examples of suitable Zwitterionic boosters of Formula5 include, cocoylamidopropylbetaine, lauroylamidopropoylbetaine, andmyristoylamidopropylbetaine. Where present, the Zwitterionic booster maybe present in the additives of the present invention in an amount in therange of from about 0.01% to about 90% by weight of the additive. Incertain embodiments, the Zwitterionic booster may be present in theadditives of the present invention in an amount in the range of fromabout 5% to about 50% by weight of the additive.

To facilitate mixing with the other components of the foamed cementcomposition, the additive of the present invention may be furthercomprise a base fluid. The base fluid may be any surfactant solubilizer,such as water, simple alcohols, or mixtures thereof, capable ofsolubilizing the above-described components of the additive.

Optionally, other additional additives may be added to the foamed cementcompositions of the present invention as deemed appropriate by oneskilled in the art, with the benefit of this disclosure. Examples ofsuch additives include, but are not limited to, lost circulationmaterials, fly ash, silica compounds, fluid loss control additives,dispersants, accelerators, retarders, salts, mica, sand, fibers,formation conditioning agents, fumed silica, bentonite, microspheres,weighting materials, and the like.

The foamed cement compositions of the present invention may be preparedin accordance with any suitable technique. In some embodiments, thedesired quantity of water may be introduced into a cement blenderfollowed by the cement component of the foamed cement compositions.Additional liquid additives, if any, may be added to the water asdesired prior to addition of the cement therewith, and additional solidadditives, if any, may be added to the water and cement, as desired,prior to mixing. This mixture may agitated for a sufficient period oftime to form a pumpable non-foamed slurry. This non-foamed slurry maythen be pumped to the well bore, and an additive of the presentinvention comprising an anionic foam stabilizer and at least one of ananionic foaming agent or a Zwitterionic foam booster may be metered intothe non-foamed followed by injection of a gas in an amount sufficient tofoam the slurry thereby forming a foamed slurry, a foamed cementcomposition of the present invention. After foaming, the foamed cementcomposition of the present invention, may be placed into a desiredlocation within the well bore and allowed to set therein.

In one embodiment, the present invention provides a method of cementingin a subterranean formation that comprises providing a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising an anionic foaming agent and an anionic foamstabilizer; placing the cement composition into the subterraneanformation; and allowing the cement composition to set therein. In someembodiments, the additive further may comprise a Zwitterionic foambooster.

In another embodiment, the present invention provides a method ofcementing in a subterranean formation that comprises providing a foamedcement composition that comprises water, a cement, a gas, and anadditive, the additive comprising a Zwitterionic foam booster and ananionic foam stabilizer; placing the cement composition into thesubterranean formation; and allowing the cement composition to settherein. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment, the present invention provides a method ofreducing the density of a cement composition that comprises providing acement composition that comprises water and a cement; adding an additiveto the cement composition, the additive comprising an anionic foamingagent and an anionic foam stabilizer; and adding a gas composition tothe cement composition. In some embodiments, the additive further maycomprise a Zwitterionic foam booster.

In another embodiment, the present invention provides a method ofreducing the density of a cement composition that comprises providing acement composition that comprises water and a cement; adding an additiveto the cement composition, the additive comprising a Zwitterionic foambooster and an anionic foam stabilizer; and adding a gas to the cementcomposition. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment the present invention provides a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising an anionic foaming agent and an anionic foamstabilizer. In some embodiments, the additive further may comprise aZwitterionic foam booster.

In another embodiment the present invention provides a foamed cementcomposition that comprises water, a cement, a gas, and an additive, theadditive comprising a Zwitterionic foam booster and an anionic foamstabilizer. In some embodiments, the additive further may comprise ananionic foaming agent.

In another embodiment, the present invention provides an additive forfoaming and stabilizing a cement composition that comprises an anionicfoaming agent and an anionic foam stabilizer. In some embodiments, theadditive further may comprise a Zwitterionic foam booster. An example ofan additive of the present invention comprises a base fluid, about 38%of an alkyl ether sulfate or an alpha-olefinic sulfonate by weight,about 7.5% to about 8% of a fatty betaine by weight, and about 7.5% toabout 8% of a fatty methyl ester sulfonate by weight.

In yet another embodiment, the present invention provides an additivefor foaming and stabilizing a cement composition that comprises aZwitterionic foam booster and an anionic foam stabilizer. In someembodiments, the additive further may comprise an anionic foaming agent.

To facilitate a better understanding of the present invention, thefollowing examples of specific embodiments are given. In no way shouldthe following examples be read to limit, or to define, the scope of theinvention.

EXAMPLE 1

Test samples were prepared that comprised fresh water, Class G cement,and air. For each test sample, an unfoamed cement composition having adensity of about 15.8 ppg was first prepared by combining the freshwater and the cement utilizing a mixing device. Predetermined amounts ofthe resultant unfoamed cement composition were then placed in fixedvolume blender jars adapted for receiving a stacked blade assembly.Next, either an additive of the present invention or a comparativeadditive consisting of mixtures of foaming agents and/or foamstabilizers were added in an amount of 2% bvow, unless otherwise noted.The formulation of the additives of the present invention and thecomparative additive are provided in Table 1, below, with the remainderbeing a base fluid. TABLE 1 Additive AOS AES Betaine¹ MES (% by (% by (%by (% by Sample No. weight) weight) weight) weight)  1 60 Not present.Not present. Not present. (comparative)  2 54 Not present. Not present.11  3 46 Not present. Not present. 23  4 41 Not present.  8 Not present.(comparative)  5 27 Not present. 14 Not present. (comparative)  6 Notpresent. Not present. 25 Not present. (comparative)  7 Not present. Notpresent. 24  5  8 Not present. Not present. 22 11  9 Not present. 60 Notpresent. Not present. (comparative) 10 Not present. 54 Not present. 1111 Not present. 46 Not present. 23 12 Not present. 41  8 Not present.(comparative) 13 Not present. 27 14 Not present. (comparative) 14 38 Notpresent.  8  8 15 24 Not present. 12 12 16 Not present. 38  8  8 17 Notpresent. 24 12 12 18 Not present. 38  8  8 19 Not present. 24 12 12¹A cocoylamidopropyl betaine was used.

After addition of the additives of the present invention or thecomparative additives to the unfoamed cement compositions in the jars,the contents were mixed at high speed. The high speed mixing by thestacked blade assembly caused each slurry to be foamed with air densityof the foamed samples, time required to form a foam, and additive addedthereto are provided in Table 2, below.

The foamed test samples were then allowed to set for 24 hours at 150° F.and atmospheric pressure after which they were subjected to compressivestrength tests in accordance with API Specification for Materials andTesting of Well Cement, API Specification 10, Twenty-Third Edition,dated April 2002. In addition, sectional densities of the resultant setfoamed test sample taken, resulting in a top, middle, and bottomdensity. The results of the testing are set forth in Table 2 below.Unless otherwise noted, where a compressive strength or sectionaldensity is not listed, the foamed test sample did not have sufficientproperties to perform the necessary tests. TABLE 2 Foamed 24 Hour FoamSample Compressive Time Density Density Strength Sample No. Additive(sec) Section (ppg) (ppg) at 150° F. (psi)  1 AOS 10 Top 10.87 10.2 414(comparative) Middle 10.83 Bottom 9.91  2 5:1, 10 Top 10.26 10.5 433AOS:MES Middle 9.76 Bottom 9.17  3 2:1, 10 Top 10.12 10.3 544 AOS:MESMiddle 9.71 Bottom 9.73  4 5:1, 5 Top 10.56 11.4 1438 (comparative)AOS:Betaine Middle 10.43 Bottom 10.51  5 2:1, 5 Top 10.27 11.34 1126(comparative) AOS:Betaine Middle 10.29 Bottom 10.57  6 Betaine 7 Top10.5 11.03 952 (comparative) Middle 10.62 Bottom 10.13  7 5:1, 5 Top9.21 10.7 974 Betaine:MES Middle 9.38 Bottom 9.83  8 2:1, 5 Top 11.2611.3 889 Betaine:MES Middle 11.22 Bottom 10.85  9 AES 5 Top 9.97 10.06281 (comparative) Middle 8.84 Bottom 8.65 10 5:1, 5 Top 9.83 10.03 535AES:MES Middle 8.91 Bottom 8.81 11 2:1, 5 Top 8.85 10.01 691 AES:MESMiddle 8.66 Bottom 8.49 12 5:1, 5 Top 8.85 10.22 422 (comparative)AES:Betaine Middle 8.66 Bottom 8.49 13 2:1, <5 Top 10.16 10.93 1010(comparative) AES:Betaine Middle 9.89 Bottom 9.80 14 5:1:1, 5 Top 10.4211.08 1442 AOS:Betaine:MES Middle 10.19 Bottom 10.31 15 2:1:1 5 Top 9.5911.53 1058 AOS:Betaine:MES Middle 9.63 Bottom 9.63 16 5:1:1 <5 Top 9.710.6 756 AES:Betaine:MES Middle 9.63 Bottom 9.49 17 2:1:1 <5 Top — 10.49— AES:Betaine:MES Middle — Bottom —  18¹ 5:1:1 <10 Top — 10.4 —AES:Betaine:MES Middle — Bottom —  19² 2:1:1 <10 Top — 10.8 1185AES:Betaine:MES Middle — Bottom —¹The additive of the present invention was included in Sample No. 18 inan amount of 0.2% bvow.²The additive of the present invention was included in Sample No. 19 inan amount of 0.5% bvow.

The above example demonstrates, inter alia, that foamed cementcompositions of the present invention that comprise fresh water and anadditive of the present invention are suitable for use in subterraneanoperations.

EXAMPLE 2

Test samples were prepared that comprised saturated saltwater, Class Gcement, and air. For each test sample, an unfoamed cement compositionhaving a density of about 17.5 ppg was first prepared by combining thesaltwater and the cement utilizing a mixing device predetermined amountsof the resultant unfoamed cement composition were then placed in fixedvolume blender jars adapted for receiving a stacked blade assembly.Next, either an additive of the present invention or a comparativeadditive consisting of mixtures of foaming agents and/or foamstabilizers were added in an amount of 3% bvow, unless otherwise noted.The formulation of the additives of the present invention and thecomparative additives are provided in Table 3, below, with the remainderbeing a base fluid. TABLE 3 Additive AOS AES Betaine¹ MES Sample No. (byweight) (by weight) (by weight) (by weight) 20 60 Not present. Notpresent. Not present. (comparative) 21 54 Not present. Not present. 1122 46 Not present. Not present. 23 23 41 Not present.  8 Not present.(comparative) 24 27 Not present. 14 Not present. (comparative) 25 Notpresent. Not present. 25 Not present. (comparative) 26 Not present. Notpresent. 24  5 27 Not present. Not present. 22 11 28 Not present. 60 Notpresent. Not present. (comparative) 29 Not present. 54 Not present. 1130 Not present. 46 Not present. 23 31 Not present. 41  8 Not present.(comparative) 32 Not present. 27 14 Not present. (comparative) 33 38 Notpresent.  8  8 34 24 Not present. 12 12 35 Not present. 38  8  8 36 Notpresent. 24 12 12  37² N/A N/A N/A N/A (comparative)¹A cocoylamidopropylbetaine was used.²The prior art additive included in Sample No. 37 was “ZONESEALANT ™2000”, commercially available from Halliburton Energy Services, Duncan,Oklahoma, that comprised an alkyl ether sulfate, a betaine, and an amineoxide in a weight ratio of about 15:4:1.

After addition of the additives of the present invention or thecomparative additives to the unfoamed cement compositions in the jars,the contents were mixed at high speed. The high speed mixing by thestacked blade assembly caused each slurry to be foamed with air. Thedensity of the foamed samples, time required to form a foam, andadditive added thereto are provided in Table 4, below.

The foamed test samples were then allowed to set for 24 hours at 150° F.are atmospheric pressure after which they were subjected to compressivestrength tests in accordance with API Specification for Materials andTesting of Well Cement, API Specification 10,Twenty-Third Edition, datedApril 2002. In addition, sectional densities of the resultant set foamedtest sample taken, resulting in a top, middle, and bottom density. Theresults of the testing are set forth in Table 4 below. Unless otherwisenoted, where a compressive strength or sectional density is not listed,the foamed test sample did not have sufficient properties to perform thenecessary tests. TABLE 4 Foamed 24 Hour Foam Sample Compressive TimeDensity Density Strength Sample No. Additive (sec) Section (ppg) (ppg)at 150° F. (psi) 20 AOS 45 Top 15.31 15.4  2280¹ (comparative) Middle15.33 Bottom 15.63 21 5:1, 45 Top 14.17 14.96 1444 AOS:MES Middle 14.25Bottom 14.34 22 2:1, 45 Top 11.72 12.8  730 AOS:MES Middle 11.75 Bottom11.86 23 5:1, 45 Top 14.54 15.06 N/A² (comparative) AOS:Betaine Middle14.42 Bottom 14.46 24 2:1, 45 Top 14.22 14.89 1946 (comparative)AOS:Betaine Middle 14.14 Bottom 14.27 25 Betaine 45 Top 12.91 13.9 1197(comparative) Middle 12.91 Bottom 13.12 26 5:1, 45 Top 12.58 13.1  957Betaine:MES Middle 12.50 Bottom 12.08 27 2:1, 45 Top 11.63 12.7  734Betaine:MES Middle 11.50 Bottom 11.34 28 AES 45 Top 10.74 11.86  504(comparative) Middle 10.56 Bottom 10.39 29 5:1, 45 Top 11.56 12.56  601AES:MES Middle 11.50 Bottom 11.25 30 2:1, 45 Top 11.88 12.85  752AES:MES Middle 11.83 Bottom 11.58 31 5:1, 45 Top 11.34 12.13  809(comparative) AES:Betaine Middle 11.14 Bottom 11.15 32 2:1, 45 Top 11.5612.11  855 (comparative) AES:Betaine Middle 11.24 Bottom 11.17 33 5:1:1,45 Top 14.37 15.2 2230 AOS:Betaine:MES Middle 14.42 Bottom 14.59 342:1:1 45 Top 13.41 13.98 1304 AOS:Betaine:MES Middle 13.29 Bottom 13.3635 5:1:1 45 Top 11.85 12.90  953 AES:Betaine:MES Middle 11.71 Bottom12.01 36 2:1:1 45 Top — 12.42 — AES:Betaine:MES Middle — Bottom — 3715:4:1 45 Top 12.03 12.74  966 (comparative) AES:Betaine:Amine Middle11.79 Oxide Bottom 11.71¹The 48 hour compressive strength at 150° F.²While the foamed test sample had sufficient properties to perform acompressive strength test, one was not performed.

The above example demonstrates, inter alia, that foamed cementcompositions of the present invention that comprise saltwater and anadditive of the present invention are suitable for use in subterraneanoperations.

Therefore, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosewhich are inherent therein. While numerous changes may be made by thoseskilled in the art, such changes are encompassed within the spirit ofthis invention as defined by the appended claims.

1. An additive for foaming and stabilizing a well cement composition,the additive comprising an anionic foaming agent and an anionic foamstabilizer.
 2. The additive of claim 1 wherein the anionic foamstabilizer comprises at least one surfactant selected from the groupconsisting of a fatty methyl ester surfactant, an aliphatic alkylsulfonate surfactant having an alkyl chain length of from about 16 toabout 22 carbons, an aliphatic alkyl sulfate surfactant having an alkylchain length of from about 16 to about 22 carbons, and combinationsthereof.
 3. The additive of claim 1 wherein the anionic foam stabilizercomprises a fatty methyl ester sulfonate surfactant.
 4. The additive ofclaim 1 wherein the anionic foam stabilizer is present in the additivefor foaming and stabilizing the foamed cement additive in an amount offrom about 0.01% to about 20% by weight of the additive.
 5. The additiveof claim 1 wherein the anionic foaming agent comprises at least onesurfactant selected from the group consisting of a sulfate surfactant, asulfonate surfactant, and combinations thereof.
 6. The additive of claim1 wherein the anionic foaming agent comprises an alkyl ether sulfatesurfactant.
 7. The additive of claim 6 wherein the alkyl ether sulfatesurfactant comprises an ethoxylated alcohol ether sulfate surfactanthaving the formula:H(CH₂)_(a)(OC₂H₄)_(b)OSO₃ ⁻X⁺ wherein a is an integer in the range offrom about 6 to about 14, b is an integer in the range of from about 3to about 10, and X is any compatible cation.
 8. The additive of claim 1wherein the anionic foaming agent comprises an alpha-olefinic sulfonatesurfactant.
 9. The additive of claim 8 wherein the alpha-olefinicsulfonate surfactant has the formula:H(CH₂)_(n)—CH══CH—(CH₂)_(m)SO₃ ⁻X⁺ wherein n is an integer in the rangeof from about 3 to about 12, m is an integer in the range of from about3 to about 12, and X is any compatible cation.
 10. The additive of claim1 wherein the anionic foaming agent is present in the additive forfoaming and stabilizing the foamed cement additive in an amount in therange of from about 30% to about 70% by weight of the additive.
 11. Theadditive of claim 1 wherein the additive for foaming and stabilizing thefoamed cement additive comprises a Zwitterionic foam booster.
 12. Theadditive of claim 11 wherein the Zwitterionic foam booster comprises atleast one surfactant selected from the group consisting of a betainesurfactant, a sulfobetaine surfactant, an amphopropionate surfactant, aglycinate surfactant, and combinations thereof.
 13. The additive ofclaim 11 wherein the Zwitterionic foam booster comprises an alkyl or analkene amidopropyl betaine surfactant.
 14. The additive of claim 13wherein the alkyl or alkene amidopropyl betaine surfactant has theformula:R—CONHCH₂CH₂CH₂N⁺(CH₃)₂CH₂COO⁻ wherein R is an alkyl or alkene chain offrom about 6 to about 18 carbons or a mixture thereof.
 15. The additiveof claim 1 wherein the additive for foaming and stabilizing the foamedcement additive comprises a Zwitterionic foam booster, wherein theanionic foam stabilizer comprises a fatty methyl ester surfactant andthe anionic foaming agent comprises an alpha-olefinic surfactant.
 16. Anadditive for foaming and stabilizing a cement composition, comprising: aZwitterionic foam booster, and an anionic foam stabilizer wherein theanionic foam stabilizer comprises a surfactant selected from the groupconsisting of a fatty methyl ester surfactant, an aliphatic alkylsulfonate surfactant having an alkyl chain length of from about 16 toabout 22 carbons, an aliphatic alkyl sulfate surfactant having an alkylchain length of from about 16 to about 22 carbons, and combinationsthereof.
 17. The additive of claim 16 wherein the Zwitterionic foambooster comprises a surfactant selected from the group consisting ofbetaine surfactant, a sulfobetaine surfactant, an amphopropionatesurfactant, a glycinate surfactant, and combinations thereof.
 18. Theadditive of claim 16 wherein the additive comprises an anionic foamingagent.
 19. The additive of claim 16 wherein the anionic foaming agentcomprises a surfactant selected from the group consisting of a sulfatesurfactant, a sulfonate surfactant, and combinations thereof.
 20. Anadditive for foaming and stabilizing a cement composition, the additivecomprising: a fatty methyl ester surfactant, an alkyl ether sulfatesurfactant, and a betaine surfactant.